With development of cellular mobile communication. Internet and multimedia service, capacity requirement of wireless communication is increased rapidly in the world, while available frequency spectrum is limited. If the using rate of communication frequency spectrum is not significantly increased, the need of communication capacity can't be satisfied. In a single antenna link system, advanced channel code, for example, Turbo code and low density check code, is used to approach Shannon channel capacity and numbers of antenna of transmitting end and receiving end are increased so as to significantly improve frequency using sate.
Multiple-Input Multiple-Out-put (MIMO) system is a technology which is firstly raised by Marconi in 1908. The MIMO system uses multiple antennas to suppress channel fading. According to the number of antennas of transmitting end and receiving end and compared with normal Single-Input Single-Output (SISO) system, the channel capacity of MIMO is increased linearly with the increasing of number of antennas. That is to say, wireless channel capacity may multiply by using MIMO channel. The frequency using rate can multiply without increasing the bandwidth and antenna transmission power,
Pre-coding technology is an important technology of downlink MIMO space reuse in Long Term Evolution (LET) system. The frequency spectrum efficiency of the system can multiply by the space reuse thereof. However the system belongs to interference limited system, thus requiring decreasing interference among antennas and users by using pre-coding technology at She transmuting end so as to Improve throughput of users and system. General pre-coding technology can be classified into two kinds; one kind is non-codebook pre-coding and the other kind is codebook based pre-coding.
In non-codebook pre-coding, a pre-coding matrix is obtained at the transmitting end. The transmitting end uses predicted channel status information to do calculations on the pre-coding matrix, generally, such as singular value decomposition, uniform channel decomposition, and the like. For a codebook based pre-coding system, in a close loop system the pre-coding matrix is obtained at the receiving end. The receiving end selects the pre-coding matrix in a predetermined codebook using the predicted channel status information and feeds the sequence number of the selected pre-coding matrix to the transmitting end; in an open loop TDD system, the transmitting end can use channel reciprocity to obtain an estimated channel response of downlink channel according to uplink pilot, thus selecting a pre-coding codebook used for downlink communication.
In fading channels, diversity becomes particularly important. In condition of optimal diversity, the error probability decreases exponentially as average signal-to-noise ratio increases. At present, bit-interleaved coded modulation (BICM) technology is applied in fading channels by 3GPP and 3GPP LIE. In the BICM, though bit-interleaved modulation makes time diversity degree of code modulation be increased, the performance of anti-fading and anti-interference of bit-interleaved coded modulation is limited since the modulation diversity is not applied. Solving the problem becomes a focus of the industry insiders.